Power transfer systems of the type used in motor vehicles including, but not limited to, four-wheel drive transfer cases, all-wheel drive power take-off units (PTU), limited slip drive axles and torque vectoring drive modules are commonly equipped with a torque transfer mechanism. In general, the torque transfer mechanism functions to regulate the transfer of drive torque between a rotary input component and a rotary output component. More specifically, a multi-plate friction clutch is typically disposed between the rotary input and output components and its engagement is varied to regulate the amount of drive torque transferred therebetween.
Engagement of the friction clutch is varied by adaptively controlling the magnitude of a clutch engagement force that is applied to the multi-plate friction clutch via a clutch actuator system. Many traditional clutch actuator systems include a power-operated drive mechanism and an operator mechanism. The operator mechanism typically converts the force or torque generated by the power-operated drive mechanism into the clutch engagement force which, in turn, can be further amplified prior to being applied to the friction clutch. Actuation of the power-operated drive mechanism is controlled based on control signals generated by a control system.
Currently, a large number of the torque transfer mechanisms used in motor vehicle driveline applications are equipped with an electrically-controlled clutch actuator that can regulate the drive torque transferred as a function of the value of the electric control signal applied thereto. In some applications, an electromagnetic device is employed as the power-operated drive mechanism of the clutch actuator. For example, U.S. Pat. No. 5,407,024 discloses use of an electromagnetic coil that is incrementally activated to control movement of a ballramp operator mechanism for applying the clutch engagement force to the friction clutch. Likewise, Japanese Laid-Open Patent Application No. 62-18117 discloses an electromagnetic actuator arranged to directly control actuation of the friction clutch.
As an alternative, the torque transfer mechanism can employ an electric motor as the power-operated drive mechanism of the clutch actuator. For example, U.S. Pat. No. 5,323,871 discloses a clutch actuator having an electric motor that controls angular movement of a sector cam which, in turn, controls pivoted movement of a lever arm used to apply the clutch engagement force on the friction clutch. Likewise, Japanese Laid-Open Publication No. 63-66927 discloses a clutch actuator which uses an electric motor to rotate one cam plate of a ballramp operator mechanism for engaging the friction clutch. Finally, U.S. Pat. Nos. 4,895,236 and 5,423,235, respectively, disclose a clutch actuator with an electric motor driving a reduction gearset for controlling movement of a ballscrew operator mechanism and a ballramp operator mechanism. Finally, commonly owned U.S. Pat. No. 6,595,338 discloses an electrohydraulic clutch actuator for controlling engagement of a friction clutch.